Factors that distinguish chondrocytes from other cells and factors active in regulating differentiating are under study. Chondronectin, the glycoprotein chondrocytes use to bind to matrix has been isolated from serum. Chondronectin is specific for chondrocytes and binds to type II collagen in the presence of proteoglycan. A new affinity purification using insolubilized glycosaminoglycan has been developed as a rapid purification for chondronectin. A protein has been isolated from testes that causes chondrocytes to dedifferentiate and prevents certain other cell types from differentiating. A general role in maintaining stem cells in an undifferentiated state is suggested.